1. Field of the Invention
The present invention relates to an information signal recording and reproducing apparatus for recording an information signal on a recording medium and for reproducing the information signal recorded on the recording medium.
2. Description of the Related Art
When a picture signal representing a still picture or a moving picture which is recorded on a magnetic recording medium or an optical recording medium as an information signal is reproduced therefrom, time-base variations may be generated in the reproduced signal. The effect of these time-base variations is the reproduction, for example, of an image representing a straight vertical bar as an image representing a deformed one. Conventionally, solution to the time-base variations problem has been found in the time-base variations correction technique in which the time-base correction is performed on the reproduced signal on the basis of a burst signal which has been added to the picture signal as a reference signal and the time-base correction technique in which the time-base correction is performed using a constant frequency signal for use in time-base correction which is multiplexed with the image signal on a frequency basis when it is recorded on the recording medium.
However, the former correction technique which employs a burst signal has a disadvantage in that stable correction is difficult when the variations such as jitter or skew are large, and that a large-scale structure is required in order to stabilize the time-base correction, increasing production cost. In the latter technique for recording a picture signal which is multiplexed with the constant frequency signal on a frequency basis, cross modulation between the constant frequency signal and the picture signal may occur, deteriorating the original picture signal.
In recent years, still video systems have been developed in which a frequency-modulated still picture signal is recorded on a 2-inch magnetic disk.
FIG. 3 shows the frequency allocation for a still picture signal recorded on the magnetic disk in the above-described still video system. As can be observed in the figure, in the still video system, the still picture signal recorded on the magnetic disk includes a luminance signal containing a synchronization signal (shown as (Y+S) in FIG. 3) which is frequency-modulated such that the tip of sync and the peak white thereof respectively produce 6 MHz and 7.5 MHz, a color-difference line-sequential signal which is frequency-modulated in the vicinity of 1 MHz (shown as (C) in the figure), and an ID (INDEX) signal which has a carrier having a frequency of about 200 KHz (accurately, 13 fH, where fH represents a horizontal synchronizing frequency) digital-modulated so that it can identify a data or a track number, these signals being multiplexed with each other on a frequency basis when they are recorded on the magnetic disk. Combination of electrical signals on a frequency basis may generate cross modulation among the respective signals. However, practically perfect recording of images is possible by the adjustment of the magnitude of a recording current of a signal and the frequency level thereof.
Thus, in the current still video system, since the luminance signal and the color-difference line-sequential signal are recorded on the magnetic disk in a state wherein they are separated on a frequency basis, as shown in FIG. 3, no burst signal is added to the luminance signal. Therefore, only the horizontal synchronizing signal (H-SYNC) having a frequency of 15.75 KHz which is added to the luminance signal can be used as a reference signal for the time-base correction conducted when the picture signal is reproduced.
However, the still video system employs as a recording medium a 2-inch magnetic disk which has a small inertial mass and which generates large jitter variations. Further, in the rotary system used for recording and reproduction, a PG pulse signal generated for each revolution of the rotary system is synchronized in phase with a vertical synchronizing signal (V-SYNC) by a phase locked loop, thereby generating large skew variations. These factors make the time-base correction utilizing the horizontal synchronizing signal insufficient.
Accordingly, a burst signal may be added to the luminance signal so as to enable accurate time-base correction to be performed when the video signal is reproduced. However, as has been stated previously, since the still video system has large variations of skew and jitter, a stable time-base correction is impossible. In order to achieve a sufficiently stable time-base correction, a large-scale structure is necessary.
Alternatively, a time-base correction employing a constant frequency signal which is multiplexed with the picture signal on a frequency basis may be performed. However, three types of signal have already been combined to form a picture signal, as shown in FIG. 3, and superimposition of a constant frequency signal may increase the possibility of cross modulation occurring, deterioration the picture signal.